"This could set up some potential fire growth similar to what we experienced when it grew exponentially last week," Piranio said. "We are working very aggressively to maintain the contingency lines."

Last week, the blaze grew to 111 square miles overnight when winds surged to more than 25 mph, the state forestry and fire protection department reported. More than 5,000 firefighters - from as far as Florida and Alaska - have worked around the clock to increase the fire containment from 10 to 18 percent by Monday.

However, a red flag warning has been issued for Tuesday and Wednesday as gusty winds are possible, said Mark Finan, the KCRA 3 First Alert weather team's chief meteorologist.

The wildfire which started on Sept. 13 continues to threaten about 21,000 structures, more than half of them homes. It has destroyed 10 homes and 22 outbuildings in the White Meadows area of Pollock Pines, according to preliminary figures released Sunday.

About 100 evacuees were allowed to return home, but some 2,700 remain under evacuation orders, state fire spokesman Daniel Berlant said. The fire also continued to threaten a key University of California, Berkeley research station that is home to scores of experiments on trees, plants and other wildlife.

The blaze was spreading smoke beyond California, with the National Weather Service issuing a "dense smoke advisory" in Reno, Nevada and Lake Tahoe on Monday some 100 miles away. Shifting winds later pushed the worst of the smoke back west.

Those winds sent the air quality index into the "very unhealthy" level for general populations in Auburn, where some schools closed, as well as in the Roseville area.

A man charged with starting the fire, Wayne Allen Huntsman, 37, pleaded not guilty to arson Friday. He remains in the El Dorado County jail on $10 million bond.